Purpose of version number install jar installation

[Peter Eisentraut <peter_e@gmx.net>]

I have long wondered what the purpose of including the version number in 
the installed name of a jar was.  I still see this requirement in the 
new policy draft.  If this is to support installing multiple versions, 
then you obviously need a lot more framework like alternatives or 
Replaces in the packages, and a package naming policy that prevents the 
packages from removing each other.  Besides that, is there any other 
point?  In any case, please include the rationale in the policy.